1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to improvements in prosthetic feet.
2. Description of the Prior Art
During normal ambulation, the first part of a foot to contact the ground is the free end of the heel. This initial contact between heel and ground is known as the xe2x80x9cheel strike.xe2x80x9d The free end of the heel is soft and thus cushions the heel strike to at least some extent. The hard bottom of the heel is the next part of the foot to strike the ground; its hardness allows it to support the entire weight of the body. The foot continues to rotate in the well-known way until the toes xe2x80x9cpush offxe2x80x9d at the end of a step.
Early prosthetic feet were quite rigid and provided little or no cushion to the impact on the ground at the moment of xe2x80x9cheel strikexe2x80x9d and little or no elastic response at xe2x80x9cpush off.xe2x80x9d The shock of impact was thus transmitted directly to the skeletal structure of the user, and the lack of elastic response forced an unnatural gait.
Perhaps the earliest prosthetic foot that provided an elastic response at heel strike and push off is disclosed in U.S. Pat. No. 4,547,913 to Phillips, assigned to Flex Foot, Inc. Multiple versions of that device have been developed. The original version is formed of a carbon fiber epoxy matrix consisting of a one-piece combination pylon upper and a one-piece sole. Mechanical fasteners interconnect the upper and the sole. In a second embodiment, the pylon is a round hollow tube and is connected by mechanical fasteners to a rectangular-shaped upper. A third version is like the first except that a standard Sach(copyright) foot adapter is employed to connect a standard prosthetic pylon. A fourth version is like the third but has a slightly different geometry. In a fifth version, an elastomeric glue connects the upper and the sole. In additional embodiments, leaf springs or hydraulic cylinders are incorporated into the prosthetic foot.
Although the developments in the art since the mid 1980s have significantly advanced the technology of prosthetic feet, the known prosthetic feet still provide little or no heel elasticity in a direction parallel to the ground. Instead, they provide elastic response in a vertical plane. Thus, although the impact at heel strike is reduced vis a vis the pre-1980""s prosthetic feet, the reduced impact is transmitted vertically to the skeletal structure of the user, and the elastic response in a vertical plane causes a four to six millimeter bounce at heel strike. This vertical response causes an unnatural walk because a healthy human heel is soft at the back or free end where heel strike occurs and is hard on the bottom so that it can support the entire weight of the body. Thus, the normal gait of a human includes a rolling motion as the back of the heel strikes the ground; there is no vertical motion causing the heel to bounce upon ground impact. Accordingly, there remains a need for a prosthetic foot that provides substantial heel elasticity in a direction parallel to the ground.
A healthy human foot rolls on the lateral part of the foot during ambulation. The medial part of the foot provides a cushion and the force required at push off. Thus, there is a smooth transition from heel strike to push off, with no vertical dynamic response of the type that could cause the foot to bounce. Prosthetic feet, however, do not provide a smooth transition from heel strike to push off. This lack of a smooth transition produces what is known in the industry as a xe2x80x9cflat spot.xe2x80x9d The presence of a flat spot between heel strike and push off produces an unnatural gait.
More particularly, the dynamic response is primarily vertical at the heel and the toe of a prosthetic foot. There is little or no component of the dynamic response in a horizontal plane as present in a healthy natural foot. The absence of dynamic response in a horizontal plane results in a step like motion going from an elastic vertical motion at heel strike to little or no support at mid-stance (the flat spot), and then again to an elastic vertical motion at push off.
There is a need, therefore, for a prosthetic foot having a dynamic response in a horizontal plane during heel strike, that provides a smooth transition between heel strike and push off to eliminate the flat spot, and that provides a dynamic response in a horizontal plane during push off.
The human foot provides a more rigid support laterally than medially. This design is advantageous because when an instability occurs, the weight of the person shifts from the rigid outer or lateral edge of the foot to the less rigid inner or medial edge. In this way, the prosthetic foot takes advantage of the presence of the natural foot, i.e., the lateral-to-medial motion experienced at the moment of an instability shifts additional support duties to the natural foot. One major drawback of the heretofore known prosthetic feet is the fact that such feet provide an exactly vertical response during ambulation with no component toward the medial section of the foot. Thus, if an instability in one foot urges the person to fall away from the natural foot, there is no shift of weight toward the medial part of the prosthetic foot as would occur in a natural foot, and the likelihood of a fall is substantially increased.
A prosthetic foot is therefore needed that has differentiated medial and lateral stiffness so that it can respond to instabilities in much the same way as a natural foot.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The long-standing but heretofore unfulfilled need for a dynamic prosthetic foot is now met by a new, useful, and nonobvious dynamic prosthetic foot that provides multiple load points. The novel foot includes a sole having a toe end and a heel end. A slot is formed in the heel end and is substantially coincident with a longitudinal axis of the dynamic prosthetic foot. The slot extends from the heel end of the sole to a preselected point in the sole.
The slot divides the heel end into a lateral heel member and a medial heel member. A pair of pylon supports are formed in the heel end and are separated from one another by the slot. The pair of pylon supports includes a lateral, posterior pylon support and a medial, anterior pylon support.
A heel extension forms a part of the lateral heel member and is integral and generally coplanar with a lateral side only of the sole. The lateral, posterior pylon support diverges from the heel extension along a preselected transverse line about mid-length of the lateral side of the sole.
The lateral heel member includes a gradual ninety degree bend formed in the sole. The gradual ninety degree bend terminates in a vertical part that forms the lateral, posterior pylon support. The lateral, posterior pylon support is disposed substantially perpendicular to the sole.
The medial heel member includes a return bend formed in the sole at the heel end thereof. The medial heel member further includes a straight section substantially parallel to the sole that extends toward the toe of the prosthetic foot. The straight section terminates in a gradual ninety degree bend formed integrally with the straight section and the gradual ninety degree bend terminates in a vertical part that forms the medial, anterior pylon support. The medial, anterior pylon support is also disposed normal to the sole.
The straight section has a length sufficient to position the medial, anterior pylon support in leading, anterior relation to the lateral, posterior pylon support.
The sole has a first convexity formed in the heel end that performs the function of the bottom of a natural heel. The sole has a concavity, performing the function of a natural arch, that is longitudinally spaced from the first convexity. A second convexity that performs the function of the ball of a natural foot is longitudinally spaced from the concavity.
The slot that divides the heel into a lateral heel member and a medial heel member may also be described as extending about to the bight of the concavity that performs the function performed by the arch of a natural foot.
A lateral, posterior pylon connector adapted to receive a lateral, posterior pylon of a prosthetic leg is secured to a trailing end of the lateral, posterior pylon support. A medial, anterior pylon connector adapted to receive a medial, anterior pylon of a prosthetic leg is secured to a trailing end of the medial, anterior pylon support.
Forces acting on the lateral, posterior pylon connector are substantially confined to the lateral, posterior pylon support and forces acting on the medial, anterior pylon connector are substantially confined to the medial, anterior pylon support. Moreover, forces acting on the lateral, posterior pylon connector are similar to the forces acting on a fibula of a natural leg and forces acting on the medial, anterior pylon connector are similar to the forces acting on a tibia of a natural leg.
The lateral, posterior pylon support has a greater thickness than the medial, anterior pylon support. The greater thickness imparts greater strength and less flexibility so that forces applied to the lateral, posterior pylon support and the medial, anterior pylon support are transferred more to the medial, anterior pylon support than to the lateral, posterior pylon support, thereby mimicking the reaction of a natural foot to forces applied thereto.
In a second embodiment, each pylon support is elongated and serves as a pylon. This eliminates the need for a pylon connector attached to the back of the pylon supports of the first embodiment. In the second embodiment, each pylon is about twenty inches (20xe2x80x3) in height and is cut to size as needed by a prosthetist at the time of fitting.
An important object of this invention is to provide a prosthetic foot having heel elasticity in a direction parallel to the ground.
Another important object is to provide a prosthetic foot having a smooth transition from heel strike to mid stance to push off.
Yet another object is to provide a prosthetic foot having differentiated medial and lateral stiffness so that an instability tends to shift weight from the lateral edge of the prosthetic foot to the medial edge thereof, just as in a natural foot.
Another important object is to provide a prosthetic foot having a heel divided into a lateral part and a medial part and where the flexing of the medial part exceeds the flexing of the lateral part.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.